Acidic tin-plating process



United States Patent 3,230,159 ACIDIC TIN-PLATING PROCESS Shigeru Yonezaki, Yawata, Fukuoka, Hazime Nitto, Ozawami-machi, Tohata, Fukuoka, and Hidejiro Asano, Tobata, Fukuoka, Japan, assignors to Yawata Iron & Steel Co., Ltd., Tokyo, Japan, a corporation of Japan No Drawing. Filed Oct. 15, 1962, Ser. No. 230,695

Claims priority, application Japan, Get. 20, 1961, 36/157,703 6 Claims. (Cl. 204-54) This invention relates to improvements in an acidic tin-plating process.

Acidic tin-plating processes are most extensively adopted in producing electroplated tin plates.

Generally, in acidic tin plating, the electrolytic plating bath consists mostly of sulphuric acid, phenol sulphonic acid, tin sulphate and a tin halide with the addition thereto of a proper additive such as, for example, diphenylol propane. However, such known additive has a drawback that its solubility in an acidic plating bath is so low that it can hardly be used.

We have confirmed that a naphthylamine represented by the general formula:

NHR

(wherein R is hydrogen or a residue of a hydrocarbon compound having 1 to carbon atoms) and its derivatives are very high in solubility in an acidic tin-plating bath and that, when said compound is added in an amount of at least about 0.1 g./l. to a plating bath, a beautiful smooth electrodeposit will be obtained on the surface of a strip.

Naphthylamine and its derivatives are very high in solubility in an acidic bath as the common property of amino compounds and can remarkably increase the workability. But, below the above mentioned concentration of 0.1 g./l., no desired efiect can be expected.

The number of the carbon atoms of the residue of the hydrocarbon compound bonded with the nitrogen atom of the naphthylarnine or its derivative is limited to 1 to 5. If it is more than 6, the solubility in the acidic bath will be reduced and it will not be desirable for industrial practree.

The luster of the electrodeposited tin plate according to the present invention is considered to be due to the fact that the N of the amino radical of the naphthylamine or its derivative will be adsorbed at the forward end of electrodeposited tin, the large atomic group of nonreactive naphthalene will prevent any later electrodeposition and a smooth electrodeposited surface will be obtained.

The naphthylamine derivatives to be used in the present invention are enumerated, for example, as follows:

IIIH(CH3) Patented Jan. 18, 1966 NH( C 11 -NH (C 2H5) NH C 5 11) The present invention shall be explained with reference to examples. However, the scope of the present invention is not intended to be limited to these examples.

Example 1 Composition of the plating bath: G./l. Phenol sulphonic acid 25 Tin sulphate 30 N-ethyl-a-naypthylamine 2 Electric current densities: 1 a./dm. 5 a./drn. and 10 a./dm. Temperature: 40 C. Thicknesses of the plating: 0.25 lb./bb., 0.5 1b./bb. and

1.00 lb./bb.

Example 2 A plating bath in which 2 g./l. of N-ethyl-a-naphthylamine in Example 1 were replaced with 2 g./l. of o:- naphthylarnine was used.

Example 3 A plating bath in which 2 g./l. of N-ethyl-a-naphthylamine in Example 1 were replaced with 2.5 g./l. of N methyl-a-naphthylamine was used.

Example 4 Composition of the bath: G./ 1. Phenol sulphonic acid 25 Tin sulphate 60 N-ethyl-fi-naphthylamine 2 Current densities: 5 a./dm. 10 a./dm. and 20 a./dm. Temperature: 40 to 60 C. Thickness of the plating: 0.25 to 1.00 1b./bb.

Example 5 A plating bath in which 2 g./l. of N-ethyl-fl-naphthylamine in Example 4 were replaced wtih 2 g./l. of {3- naphthylamine was used.

When the composition was electrodeposited on a strip under the above mentioned conditions, a tin plate having a milk-White lustrous surface was obtained. When this plate was subjected to a tin-melting treatment by direct electric heating, a favorable plate was obtained.

Even when the composition of the plating bath in the process of the present invention is varied in a range considerably wider than the above mentioned compositions, a lustrous surface can be obtained.

What we claim is:

1. In a process for producing electroplated tin plate in an acidic tin-plating bath containing an additive, the improvement wherein the additive is a naphthylamine of the formula NHR NER

wherein R is a member selected from the group consisting of H and alkyl with 1 to 5 carbon atoms.

3. An improvement according to claim 1, wherein the naphthylamine is N-ethyl-a-naphthylamine.

4. An improvement according to claim 1, wherein the naphthylamine is a-naphthylamine.

5. An improvement according to claim 1, wherein the naphthylamine is N-ethyl-[i-naphthylamine.

6. An improvement according to claim 1, wherein the naphthylamine is B-naphthylamine.

References Cited by the Examiner UNITED STATES PATENTS 2,446,716 8/1948 Nachtman 20443 2,450,794 10/ 1948 Harris 20454 2,552,920 5/1951 Allen 20454 2,598,486 5/1952 Andrews 20454 JOHN H. MACK, Primary Examiner. 

1. IN A PROCESS FOR PRODUCING ELECTROPLATED TIN PLATE IN AN ACIDIC TIN-PLATING BATH CONTAINING AN ADDITIVE, THE IMPROVEMENT WHEREIN THE ADDITIVE IS A NAPHTHYLAMINE OF THE FORMULA 